The bighorn sheep’s dramatic history includes reaching near extinction and making a significant recovery with the help of conservation efforts.
Crossing over the Bering land bridge from Siberia, the species' population in North America peaked in the millions. Much as the bison did for Native American tribes in the Great West, bighorn sheep were sources of food, clothing, and tools for tribes in the mountainous regions of the west. Petroglyphs featuring bighorns are among the most common images across all western U.S. states.
By 1900, encroachment from human settlers diminished the population to several thousand. Bighorn sheep have made a comeback thanks to a conservation movement supported by President Theodore Roosevelt, reintroductions, national parks, and managed hunting. Unfortunately, some subspecies, such as Ovis canadensis auduboni of the Black Hills, were driven into extinction.
Historic 1930s campaigns to save the desert bighorn sheep have resulted in the establishment of two bighorn game ranges in Arizona: Kofa National Wildlife Refuge and Cabeza Prieta National Wildlife Refuge.
Hunters, not taxes, pay for bighorn sheep conservation and restoration efforts. Funds are derived from the purchase of hunting licenses and tags and indirectly through an excise tax on sporting goods.
Today and in the past, the efforts of conservation groups have also served to increase awareness and "petition" to place certain sub-species like the Sierra Nevada bighorn sheep on the Endangered Species List.
Description: The bighorn sheep is one of two species of wild sheep in North America with large horns, the other being the Dall sheep (Ovis dalli).
Its compact body is muscular, with chocolate brown fur trimmed in white on the muzzle, rump and belly. Most weigh 160-250 pounds, but rams may weigh over 350 pounds and stand around 40 inches at the shoulder.
Their wide-set eyes are situated well forward on the head, providing a wide arc of exceptional vision. The bighorn sheep's keen eyesight, hearing, and sense of smell help it detect and avoid predators.
The latest science shows that "bighorn sheep" is one species, with 3 living subspecies:
- Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis)
- Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae), formerly California Bighorn Sheep
- Desert Bighorn Sheep (Ovis canadensis nelsoni)
Horns & Hooves: Large, curved horns, borne by the males, or rams, can weigh up to 30 lb (14 kg) - as much as the rest of the bones in the male's body. Older rams have massive horns that can grow over 3 feet long with more than one foot in circumference at the base.
Females, or ewes, also have horns, but they are short with only a slight curvature. Both rams and ewes use their horns as tools for eating and fighting.
Although not as agile as mountain goats, bighorn sheep are well-equipped for climbing the steep terrain that keeps their predators at bay. The outer hooves are modified toenails shaped to snag any slight protrusion, while a soft inner pad provides a grip that conforms to each variable surface.
Habitat and Range: Bighorn sheep live in the western mountainous regions of North America, ranging from southern Canada to Mexico.
Their steep mountainous habitat, with ledges sometimes only 2 inches wide, provides cover from predators such as coyotes, golden eagles, mountain lions, bears, and Canada lynx. The sheep are important food sources for these large predators.
Most populations undergo seasonal movements, generally using larger upland areas in the summer and concentrating in sheltered valleys during the winter.
Behavior: Mature males spend most of their year in bachelor flocks apart from groups of females and young sheep. Young females generally remain in their mother's group (led by an older ewe) for life. All ewes are subordinate to even young rams with bigger horns.
Males depart their mother's group around 2 to 4 years of age and join a group of rams. This is sometimes a tough time of wandering until the young rams find a male group and they will sometimes take up with other species out of loneliness.
Bighorn sheep groups protect themselves from predators by facing different directions, allowing them to keep watch on their surroundings.
Diet: As ruminants, grass-eating bighorn sheep have a complex four-part stomach that enables them to eat large portions rapidly before retreating to cliffs or ledges where they can thoroughly re-chew and digest their food, safe from predators. Then bacteria takes over, breaking down plant fibers for digestion. The sheep also absorb moisture during this digestive process, enabling them to go for long periods without water.
Lifespan: Longevity depends on population status. In declining or stable populations, most sheep live over 10 years. Even in areas where no hunting occurs, females rarely make it past 15 and males rarely live beyond 12. Juvenile mortality is variable and can be quite high, ranging from 5 to 30%. Sheep between 2 and 6 years old have low mortality.
Reproduction: It is during the mating season or "rut” that the rams join the female groups and engage in fierce competition to establish access rights to ewes. Their dominance hierarchy is based on age and size (including horn size), which usually prevents rams younger than seven years old from mating. Younger males will mate sooner if dominant rams in their group are killed.
Mating competition involves two rams running toward one another, at speeds around 40 mph, and clashing their curled horns, which produces a sound that can be heard a mile away. Most of the characteristic horn clashing between rams occurs during the pre-rut period, although this behavior may occur to a limited extent throughout the year.
Featured Video: Peak to Peak
Researcher Jack Hogg discusses bighorn sheep behavior and how future generations could be affected by climate change.
Peak to Peak from Conservation Media on Vimeo.
Mountain lions, coyotes, wolves and bears will all kill mountain sheep if given the opportunity, but chasing the sheep in the cliffs is rarely successful.
Disease usually takes a far higher toll among bighorns than predators.
As sure-footed as they are, bighorn sheep sometimes slip and fall from the cliffs or are struck by falling rocks.
Poaching of large, trophy males.
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Battle for Bighorns
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Conservation efforts seem to be paying off for bighorns in the West